Despite the increased data transmission rates that are possible in landline and fiber optic networks, many communication systems employ radio frequency links to transmit and receive information. Such radio frequency links are used for point to point communication between telephone switches, between cellular telephone sites, or in satellite communication. For some high speed data communication applications some radio frequency links employ relatively high power transceivers, which may operate in the microwave frequency range.
A radio frequency (rf) transceiver typically includes a high power transmitter that broadcasts rf signals to a remote location and a receiver that detects weaker rf signals that are broadcast from the remote location. In a transceiver where the receiver is tuned to a frequency that is near the carrier frequency of the transmitter (or a multiple thereof), the transmitter may generate stray signals that could leak into the receiver and saturate it. When saturated, the receiver is generally unable to detect the rf signals that are transmitted from a remote location.
One prior art approach used to prevent the stray rf signals from leaking into a receiver is to physically separate the transmitter and the receiver. For example, a transmitter assembly may be placed in a separate cavity and shielded from the receiver assembly. While the physical separation of the transmitter assembly and the receiver assembly in two different cavities reduces the rf leakage problem, this approach typically increases the cost and overall dimensions of the radio transceiver.
Alternatively, attempts have been made to place the transmitter and receiver circuits on the same printed circuit board, while employing traditional shielding methods such as enclosing portions of the transmitter in a grounded metal shell or placing grounding holes or vias between the transmitter and receiver to isolate stray rf signals. However, such conventional isolation techniques generally do not prove effective in providing the desired level of isolation for satisfactory operation of a transceiver when operated at high power in certain applications.
Accordingly, there is a need for a better isolation technique for use in circuit boards to reduce the level of leakage signals from one portion of the board to another.